1. Field of the Invention
The present invention relates generally to a TV lens drive unit, and more particularly to a TV lens drive unit which controls the zooming of a zoom lens used in an ENG camera, etc.
2. Description of Related Art
In an ENG lens used for a broadcast camera, etc., a lens drive unit is attached to the side of a lens barrel, and a rotational driving force of a motor, which is arranged in the drive unit, drives a focus ring, a zoom ring, and an iris ring in the lens barrel to adjust a zoom, a focus and an iris, respectively.
The lens drive unit performs the zooming with a zoom seesaw control switch (hereinafter referred to as a seesaw switch) and a zoom rate demand unit. The zoom rate can be adjusted in accordance with the operated amount of the seesaw switch and a thumb ring of the zoom rate demand unit.
To control the zooming at a constant rate, however, it is necessary to keep the depth (the operated amount) of the seesaw switch or the thumb ring constant with fingers. While a cameraman is shooting with an ENG camera on the shoulder, it is difficult to control the zooming at a constant rate. In particular, the pressed amount of the seesaw switch, etc. must be kept constant for a long period of time in order to maintain the slow rate, and such an operation is difficult.
The present invention has been developed in view of the above-described circumstances, and has as its object the provision of a TV lens drive unit which is able to control the zooming at a constant rate by a simple operation and reduce the difficulties during the operation.
To achieve the above-described objects, a TV lens drive unit which moves a variable frame lens group of a TV lens with a motor to thereby adjust a zoom, the TV lens drive unit comprising: zoom control means for designating a telephoto/wide zoom direction and a zoom rate; storage means for storing the zoom direction and the zoom rate, designated by the zoom control means when switch means is operated, in response to the operation of the switch means during the operation of the zoom control means; and motor control means for invalidating the zoom direction and the zoom rate designated by the zoom control means in response to the operation of the switch means during the operation of the zoom control means, and running the motor so that the zoom rate can be constant in accordance with the designation of the zoom direction and the zoom rate stored in the storage means.
According to the present invention, if the switch means is operated when the zoom control means control the zooming by designating the zoom direction and zoom rate, the designated zoom direction and zoom rate when the switch means is operated are stored in the storage means. Then, a command from the zoom control means is invalidated, and the zooming continues at the stored zoom rate in the stored direction. It is therefore possible to easily maintain the zoom rate constant by operating switch means during the operation of the zoom control means.
Moreover, the above-described TV lens drive unit is provided with a detection means which detects that the zoom position is close to the telephoto end or the wide end, and a reducing means which reduces the zoom rate in proximity to the telephoto end or the wide end in accordance with the detection of the detection means. It is therefore possible to prevent a sudden stop at the telephoto end or the wide end, and the lens can stop naturally at the zoom end.
Furthermore, the control member of the switch means may also serve as a control member of a switch means relating to another function such as a return switch.